The present invention relates to the field of detection and sensing by means of electronic sensors or detectors, in particular metal objects, and relates to a proximity or presence switch arrangement operating in accordance with the inductive principle.
Switch arrangements of this type are predominantly used in conjunction with automated operating devices (such as robots) or with safety devices, in particular in the automotive industry.
The inductors present in these switching arrangements are stored with an oscillating electrical signal and thus develop a changeable magnetic sensing field, the nature of which depends on the nature of the inductor and the features of the stored signal.
If a metal object enters the range of this field the latter is changed by the damping effects of this object. This change is then detected and evaluated in order to optionally initiate actions if predetermined conditions occur or are exceeded, such as changes in the switching state of connected switching amplifiers.
If the switching arrangements are used in an industrial environment they are exposed to influences which are disruptive to measuring and sensing, such as metallic powder or welding particles which can accumulate on the housing.
A switch arrangement of the type mentioned at the outset is already known in which an attempt is made to compensate for the influences disruptive to measuring by an additional arrangement.
However, this is a complex structure in which the compensating component itself is exposed to disruptive influences and thus cannot always optimally compensate.
In addition it should be mentioned that a constant energy supply is required in all existing aforementioned arrangements and the excitation signals are matched to the inherent oscillating frequency of the oscillating circuit containing the inductor.